RabbitMQ: Adding the queue_delivery_metrics OpenMetrics endpoint

[edgrz]

What does this PR do?

As part of /detailed metric endpoints, there's a queue delivery metrics one (docs), that were not integrated yet into datadog agent. This PR integrates them.

Motivation

I prepared the DD agent to scrape such /detailed?family=queue_delivery_metrics but none of them were appearing in DD. So, looking into the source code I realize there was yet no mapping for there.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.09%. Comparing base (60b6a09) to head (52037e4).

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
rabbitmq	95.59% <ø> (ø)
solr	?

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[dkirov-dd]

Hello @edgrz, thank you for your contribution!
Could you add these metrics to the metadata.csv?

It seems like they were added in this commit: rabbitmq/rabbitmq-server@bb93e71
Out of curiosity, which version of RabbitMQ are you using? Are you sure it exposes them?

Lastly, it would be great to include the new metrics in the tests as well!